Wideband transmission with high spectral efficiency and high mobility is desirable for future wireless communications. Promising techniques to achieve such wideband transmission include an orthogonal frequency-division multiplexing (OFDM) technique.
A traditional OFDM-based communication system uses a plurality of closely-spaced orthogonal subcarriers to carry data. The data may be allocated on a plurality of parallel subchannels, one for each of the subcarriers. Each of the subcarriers may be modulated with a conventional modulation scheme, e.g., quadrature amplitude modulation, at a relatively low symbol rate. In addition, an inverse fast Fourier transform (IFFT) may be performed on OFDM symbols representing the data on a transmitter side, e.g., at a base station, and a fast Fourier transform (FFT) may be performed to recover the OFDM symbols on a receiver side, e.g., at a mobile station.
Traditionally, the base station allocates available resources, e.g., time and frequency resources, for the mobile station to receive data from, or transmit data to, the base station. The base station further uses a control channel to indicate to the mobile station the allocated resources.
The available resources may include a plurality of resource units (RUs). An RU typically comprises a first plurality of consecutive subcarrier frequencies and a second plurality of consecutive times corresponding to respective OFDM symbols, and is a basic unit for resource allocation. For example, in the IEEE 802.16 standard, 24 RUs may be used to perform resource allocation if the communication system has a 5-MHz bandwidth, 48 RUs may be used to perform resource allocation if the communication system has a 10-MHz bandwidth, and 96 RUs may be used to perform resource allocation if the communication system has a 20-MHz bandwidth.
The base station may partition the available resources into a plurality of subbands each including multiple RUs, and a plurality of minibands each including, e.g., one RU, to reduce feedback overhead. Typically, the subbands are suitable for frequency selective allocation as the subbands provide a contiguous allocation of RUs in frequency, and the minibands are suitable for frequency diverse allocation as the minibands are permuted in frequency.
FIG. 1 illustrates a traditional method 100 for the base station to partition available resources into a plurality of subbands 102. Based on the method 100, the base station partitions the available resources into the plurality of subbands 102 each including four contiguous RUs.
FIG. 2 illustrates a traditional method 200 for the base station to perform resource allocation for a plurality of mobile stations, e.g., MS0, MS1, . . . , and MS7. The base station may partition available resources including a plurality of RUs, referred to herein as physical RUs (PRUs) 202, each represented by a small block in FIG. 2, into a plurality of subbands 204 and a plurality of minibands 206. Each of the subbands 204 may comprise multiple contiguous PRUs, e.g., four contiguous PRUs, and each of the minibands 206 may comprise one PRU.
The base station may further group the PRUs 202 in the subbands 204 into a subband group. The PRUs 202 in the subband group are also known as contiguous resource units (CRUs) 208, because they are contiguous across localized resource allocations. The base station may also group the PRUs 202 in the minibands 206 into a miniband group and perform permutation on those PRUs. The permuted PRUs in the miniband group are also known as distributed resource units (DRUs) 210, because they are spread across distributed resource allocations.
The CRUs 208 and the DRUs 210 form logical resource units (LRUs) 212. The base station may perform resource allocation to each of the mobile stations based on individual LRUs, or on a whole subband. For example, the base station may allocate individual LRUs to a mobile station, e.g., MS0, MS1, MS2, MS4, MS5, MS6, or MS7. These LRUs for the corresponding MSs may be indicated by basic assignment A-MAP information elements (IEs). Also for example, the base station may allocate one or more subbands to a mobile station, e.g., MS3. These subbands may be indicated by a subband assignment A-MAP information element (IE). The basic and subband assignment A-MAP IEs are located in an A-MAP region, which typically consists of the first several DRUs.
Further, for example, MS3 may only need to perform data transmission at a relatively low data transmission rate, such as when running a Voice over Internet Protocol (VoIP) application or a gaming application. As a result, it may be inefficient for the base station to allocate the whole subband to MS3.